1. Field of the Invention
This invention relates to alternators and alternator-starters for motor vehicles.
2. Description of Related Art
It is known from the document EP-0 425 132 and the corresponding document U.S. Pat. No. 4,959,577 to provide a motor vehicle alternator having a rotor which includes polar wheels with interleaved horns. Grooves are formed in the side faces of the horns in facing relationship with each other, and magnets are lodged in these grooves to improve the magnetic properties of the rotor. In order to form the grooves, the pole wheels are assembled together, thereby interleaving the horns, and then a milling tool is traversed along each space between the horns, machining the two grooves in facing relationship with each other in a single pass, the milling tool being extracted through the longitudinal end of the groove that was last machined. However, with this method, the horns have to be disposed at a good radial distance away from the heart of the rotor, otherwise there is a danger that the motion of the milling tool will damage parts of the heart of the rotor that project most prominently, such as a length of wire, the capstan member by which the wire is positioned, and so on. However, this results in the rotor and the alternator having a large radial dimension.
One object of the invention is to reduce the volume of the alternator, or to preserve its volume when elements are added to it.
With a view to achieving this object, the invention provides a vehicle alternator comprising a rotor having interleaved polar horns, at least one of the horns having, facing another one of the horns, a side face which has a profiled groove, wherein the groove has a longitudinal end which is blind in a longitudinal direction of the groove.
Thus, by locating the blind end close to the portions of the heart of the rotor that project by the greatest radial amount towards the horns (the capstan member, wire, . . . ), it is possible to locate the horns radially closer to the heart so as to reduce the overall diameter of the rotor and the volume of the alternator. Though they are blind, the grooves are able to receive an interpolar magnet. In addition, the blind end provides an abutment which facilitates the longitudinal positioning of the magnet in the grooves, and, usually, its lateral positioning.
Preferably, the two horns have respective grooves facing each other and with blind ends.
Preferably, the blind ends are in facing relationship with each other.
Preferably, the alternator includes a magnet which is received in the grooves between the or each pair of horns.
Preferably, the magnet has at least one face in the form of a sector of a cylinder contiguous with a side face and with an end face of the magnet.
Thus, since the closed end of the groove is itself also in the form of a sector of a cylinder, the longitudinal and lateral positioning of the magnet in the grooves is facilitated, especially as, for the sector of a cylinder of the magnet, the same radius of curvature is chosen as for the sector of a cylinder of the groove. In addition, the magnet thus occupies most of the available space.
Preferably, the magnet has two faces in the form of cylindrical sectors which are contiguous to a common longitudinal end of the magnet.
Thus, this configuration facilitates introduction of the magnet into the grooves.
Preferably, the alternator includes a lamination, which is for example made of a material softer than the material of the magnet, and which extends within the grooves.
The said lamination contributes to the taking up of clearances between the magnet and the grooves.
Also in accordance with the invention, there is provided a method of making a vehicle alternator, comprising a rotor which includes interleaved polar horns, wherein a profiled groove is formed on at least one side face of one of the horns which is adapted to be in facing relationship with another one of the horns, and the groove is formed with a longitudinal end which is blind in a longitudinal direction of the groove.
Preferably, after the horns have been interleaved, two grooves are machined in the side faces of two horns facing each other, both in the same pass of a tool.
Preferably, the grooves are machined starting from an axial end of the grooves which is open in the longitudinal direction, and the tool is then extracted from the grooves through the open end.